1022 PELECYPODA. [Eulfimellibrnnchia. 



from the front part by a shallow groove, it is ornamented with dis- 

 tant wavy growth -lines, crossed posteriorly by fine radiate striae ; 

 auricle with faint growth-lines only. Epidermis thin, horny. Colour 

 yellowish-white with a narrow light-brown streak descending from 

 the beaks to the ventral point. Interior : Below each of the rounded 

 beaks there is a very narrow horizontal lamella ; the posterior part is 

 strongly callous, a prominent ridge indicating the anterior limit of the 

 auricle. Apophysis long and slender, the edges somewhat irregular, 

 presenting its broader side to the inner disc, the lower end not swollen. 

 Tubercle at the lower edge stout, with 2 sharp ridges, one extending 

 a short way up the anterior end of the body, the other up the middle 

 of it. Margins : Both anterior margins are thin and sharp, smooth, 

 the lower edge not microscopically denticulate ; posterior margins 

 smooth, rather blunt. Pallets long and narrow, tapering slowly to- 

 wards the apex, flat on the inner side, rounded on the outer, apparently 

 composed of imbricating and pectinate joints, and with a moderately 

 long cylindrical handle. When disarticulated the pallet is seen to be 

 composed of a central stalk to which are strung laterally compressed 

 little funnel-shaped cups, flat on one side, the largest cups at the 

 bottom ; their number varies from 25 to 30, and the length of the 

 pallet is about 20 mm. 



Measurement of a shell from Auckland Harbour : Diameter- 

 Ant. -post., 9mm. ; dorso-ventral. 11 mm. : transverse diameter of one 

 valve, 5-5 mm. 



Hob. Auckland Harbour (H. S.) ; Palliser Bay, in a small piece 

 of timber dredged in 20 fathoms (E. R. Waite). The type is from 

 Port Phillip, Victoria. It also occurs in Tasmania, and Callao, Peru. 



SUBORDER 8. ANATINACEA. 



Hermaphrodite Eulamellibranchia, in which the ovaries and testes 

 are distinct and have separate orifices. The toot generally rather 

 small. The mantle frequently presents a fourth orifice. The external 

 gill-plate directed dorsally, and devoid of a reflected lamella. Hinge 

 of. shell without teeth. 



Fain. THRACIID^E, Dall. 



Animal : Mantle with a fourth pallial orifice ; the pedal orifice 

 elongated ; siphons rather long, quite separate, and completely re- 

 tractile and invertible ; monoecious ; marine. 



Shell earthy and cellule-crystalline, not nacreous ; inequivalve, 

 thin, edentulous, often with a granular surface ; ligament and resiliuin 

 chiefly external, opisthodetic, parivincular, seated on posteriorly 

 directed nymphse ; area absent, beaks usually entire ; valves nearly 

 dosed, with pallial sinus. 



Jura to Recent. 



